A heat exchange membrane is used for, for example, an air-conditioning system, and can allow heat exchange without mixing indoor air and outdoor air with each other. In recent years, a total heat exchange membrane is used that can exchange not only sensible heat but also latent heat (humidity). A heat exchanger is often installed inside structures, such as buildings, factories, and houses, and therefore, the heat exchange membrane is also required to have flameproofness and flame retardancy for fire prevention.
As a total heat exchange membrane, for example, a heat exchange membrane formed of paper is adopted, and the paper heat exchange membrane is impregnated with a hydrophilic flame retardant. The paper heat exchange membrane, however, has a low water resistance. For example, condensation water may become attached to the heat exchange membrane, depending on the use conditions of the heat exchanger. If the condensation water is frozen, the paper heat exchange membrane may be torn. Further, the condensation water causes the elution of the flame retardant, and therefore, the flame retardancy and the latent heat exchange performance are deteriorated.
To prevent a tear caused by condensation water, there has been proposed to use a layered product, in which a continuous layer of a moisture-permeable resin is formed on the surface of a porous fluororesin membrane, as a total heat exchange membrane (Patent Documents 1 and 2). The layered product is usually reinforced with a nonwoven fabric or other materials. Further, to improve the flame retardancy of the layered product, Patent Document 2 also discloses blending a flame retardant into the moisture-permeable resin layer.
Meanwhile, there has been disclosed that in a dust removal filter composed of an electrofilter and a flame-retardant nonwoven fabric, a flame retardant is blended also into an adhesive by which the electrofilter and the flame-retardant nonwoven fabric are attached to each other (Patent Document 3). The dust removal filter has air permeability, but a conventional moisture-permeable separating membrane material does not have air permeability; therefore, these materials belong to technical fields that are quite different in whether each of them has air permeability or not.